1. Field of the Invention
This invention relates to decaffeinating aqueous extracts of tea and to the resulting tea product.
2. Description of the Prior Art
During the enzymatic oxidation of green tea leaves (commonly referred to as "fermentation"), a number of substances, collectively referred to as "tannins", are produced. Fermentation for extended periods will provide the maximum amount of tea tannins; partial fermentation will provide only a portion of the tannins which a given tea is capable of producing. Also, aqueous tea extracts can be oxidized in the manner described in U.S. Pat. No. 2,863,775 to provide increased tannins content.
Tea tannins, including those that are soluble and those that are partially or wholly insoluble in cold water, are largely responsible for the characteristic astringency of tea and constitute a significant portion of soluble tea solids. They thus constitute a desired part of a commercial tea product, be it in the form of a full strength brew, concentrated aqueous extract or dry soluble powder.
U.S. Pat. No. 2,963,368 describes a process for preparing a cold-water-soluble tea extract from which a portion of the caffeine and tannins have been removed. According to that process, a concentrated tea extract is cooled, thereby precipitating the insoluble tea tannins complexed with an unspecified quantity of the caffeine present in the extract. The insoluble complex is removed from the remaining portion of the extract by centrifugation or other mechanical means and is never restored, resulting in a disclosed loss of about 10% of the tea solids, including the tannins. Thereafter a solubilizing or suspending agent is added to the centrifuged extract to maintain the remaining caffeine and tannins in solution or suspension. This procedure of discarding a substantial portion of the tannins is not only disadvantageous from the standpoint of the quality and flavor of the decaffeinated extract (since tea tannins contribute significantly to the organoleptic profile of the product), but it is also unnecessarily wasteful of economically valuable tea solids. Moreover, the finished product contains an additive not found naturally in tea (gum, glycerol, etc.).